Binding characteristics of chemosensory proteins from Spodoptera exigua with different insecticides

It has been reported that insect chemosensory proteins (CSPs) can bind insecticides and mediate insecticide resistance. However, there has been no systematic study on the binding spectra of CSP to different structures of insecticides. Therefore, we analyzed the expression patterns of Spodoptera exigua chemosensory proteins (SeCSPs) and their expression differences between resistant and susceptible populations. CSPs with significant expression differences were selected for prokaryotic expression, and fluorescence competitive binding assays were adopted to comprehensively analyze, for the first time, the binding affinities of these proteins to 35 insecticides with distinct structural types. The results showed that most SeCSP genes were highly expressed in the head, followed by the cuticle and hemolymph. In resistant populations of S. exigua, the expression levels of SeCSP6 (2.41-fold), SeCSP10 (30.73-fold), SeCSP11 (2.71-fold) and SeCSP18 (2.74-fold) were significantly upregulated, while SeCSP15 (0.48-fold) and SeCSP17 (0.47-fold) were markedly downregulated. Using fluorescence competitive binding assays, we discovered for the first time that SeCSP10 and SeCSP17 exhibit moderate and high binding affinities for phoxim, with Ki values of 14.46 μM and 9.31 μM, respectively. By contrast, chlorpyrifos only shows moderate binding affinity to SeCSP17 (Ki = 10.37 μM). Molecular docking further revealed that hydrophobic interactions and hydrogen bonds are the primary forces maintaining the binding between SeCSP proteins and insecticides. This study clarified the binding characteristics of SeCSP isoforms toward insecticides with different structures, and provided a theoretical reference for investigating the involvement of SeCSPs in insecticide resistance.